The present invention generally relates to mechanisms for preventing uneven take-up of tape, and more particularly to a mechanism for preventing uneven take-up of tape in a magnetic tape unit.
Recently, the size of magnetic tape units has been reduced considerably, and it has become impossible to provide a long tape path for the purpose of stabilizing the tape transport. For this reason, it has become necessary to provide a mechanism for preventing uneven take-up of tape to guarantee stable tape transport.
FIG. 1 shows an example of a mechanism for preventing uneven take-up of tape (hereinafter simply referred to as an uneven tape take-up preventing mechanism) of a conventional magnetic tape unit in a plan view, and FIG. 2 shows a side view of the uneven tape take-up preventing mechanism when viewed in a direction A in FIG. 1.
In FIGS. 1 and 2, a take-up reel 1 for taking up a tape 2, and a roller guide 3 are shown. The roller guide 3 is provided with a lower flange 5 which is fixed on the lower side thereof, and an upper flange 4 which is provided on the upper side thereof. This upper flange 4 is movable along the axis direction of the roller guide 3, and is urged towards the lower flange 5 by a spring (not shown). The top edge of the tape 2 is pushed by the upper flange 4 and the lower edge of the tape 2 slides against the lower flange, so that the tape 2 is positioned in a direction perpendicular to a transport direction of the tape 2.
A base part of an arm 6 is pivotally supported on a magnetic tape unit body. A spring 7 is fit around a rotary shaft of the arm 6. One end of this spring 7 is fixed to the magnetic tape unit body, and the other end of this spring 7 is fixed to the arm 6. Hence, a free tip end of the arm 6 is urged to pivot towards the take-up reel 1. An arm roller 8 is rotatably supported on the tip end of the arm 6. The arm roller 8 has a contact region 8a which makes contact with approximately the central part of the tape 2 which is taken up on the take-up reel 1, so as to prevent uneven take-up of the tape 2 by the take-up reel 1.
Next, a description will be given of the uneven tape take-up preventing mechanism having the above described construction.
As described above, the arm roller contact region 8a, which is rotatably provided on the tip end of the arm 6, makes contact with the tape 2, which is taken up on the take-up reel 1, by the action of the spring 7. As a result, the tape 2 which is taken up on the take-up reel 1 is prevented from moving in a direction perpendicular to the transport direction of the tape 2, and it is possible to evenly take up the tape 2 on the take-up reel 1.
However, when the tape 2 is taken up on the take-up reel 1, air is also taken up with the tape 2. For this reason, when the tape 2 is taken up on the take-up reel 1 together with the air, the air is pushed out in the direction (up and down in FIG. 2) perpendicular to the transport direction of the tape 2 because the contact region 8a of arm roller 8 pushes against approximately the central part of the tape 2 which is taken up on the take-up reel 1.
If the force of the spring which urges the upper flange 4 of the roller guide 3 downwards in FIG. 2 is relatively small, the tape 2 moves up against the force exerted by this spring due to the escaping air. This upward movement causes uneven take-up of the tape 2 on the take-up reel 1.
On the other hand, if the force of the spring 7 is relatively small, the tape 2 also moves up and down, that is, in the direction perpendicular to the transport direction of the tape 2, due to the escaping air. This up and down movement of the tape 2 also causes uneven take-up of the tape 2 on the take-up reel 1.
Therefore, in order to prevent the uneven take-up of tape, it is necessary to set the forces exerted by the spring of the roller guide 3 and/or the spring 7 to relatively large values. However, if the pushing force of the upper flange 4 is large, the top edge of the tape 2 can easily be damaged. Furthermore, if the pushing force of the arm roller 8 on the tape 2 is large, a mark formed by the roller arm 8 may remain on the back surface of the tape 2, resulting in another problem.